Signal transmitter comprising a hall sensor integrated in a master cylinder

ABSTRACT

The present invention relates to a position indicator for displaying the position of a piston ( 3 ) within a cylinder ( 1 ) as part of a piston-and-cylinder assembly ( 1, 3 ) in a brake system. The provision of a Hall element for a hydraulic generating cylinder is known in the art, with the Hall sensor mounted on the cylinder and a ring magnet mounted on the piston. An object of the invention is to describe a position indicator for a brake system, which has a simple construction and is able to provide signals relating to the position of the brake pedal relatively rapidly. This object is achieved because a Hall element of a Hall sensor ( 12 ) is placed in the cylinder wall ( 1 ) of the master cylinder, and because a magnetic zone ( 9 ) is arranged in the piston-and-cylinder assembly so that the Hall element responds to the piston movement within the cylinder.

[0001] It is important for many control operations and alarm actions toknow about the current position of an actuating element. Thus, e.g. theposition of the brake pedal or the pedal's movement is characteristic ofthe driver's desire to slow down the vehicle. In this respect, both thecourse of the movement of the brake pedal and the position of the brakepedal can give an indication to what extent the driver wishes to brakethe vehicle. Therefore, suggestions have been made to measure theposition, the travel, or the variation of travel of the brake pedal bymeans of sensors. The measured values are then introduced into theregulating device of a brake system. The measured values may further besent to a light display indicating to the other traffic members that thebrake of a vehicle is being applied. Presently customary brake lightswitches are hence arranged at the pedal. The electrical coupling inthis zone is disadvantageous. It is also a shortcoming that this type ofswitches is not particularly reliable. Further, pressure switchesarranged in the tandem master cylinder have been disclosed which areused as brake light switches. It is unfavorable that the signal isemitted quite late.

[0002] German application DE-OS 19915832 discloses equipping a hydraulicgenerating cylinder with a Hall element, with the Hall sensor beingmounted on the cylinder and a ring magnet being mounted on the piston.Therefore, the present invention is based on a position indicator of thetype that can be taken from the preamble of the main claim. An object ofthe present invention is to describe a position indicator for a brakesystem, which has a simple design and is able to provide signalsdescribing the position of the brake pedal in a comparatively quickmanner.

[0003] This object is achieved by the combination of features that canbe taken from the characterizing portion of the main claim. Thus, thepresent invention in principle resides in mounting a Hall sensor to themaster cylinder of a brake system. A wearfree quick-action display isthereby achieved which mainly describes the position or movement of thepedals. A special advantage of the present invention, among others,includes that a display is ensured even if the brake is applied due tothe movement of the piston in the master cylinder, without thisnecessarily corresponding to the position of the pedal. This feature maye.g. occur when the travel of the pedal is not identical to the travelof the piston in the master cylinder due to tolerances or lost travels.Another possibility involves that the brake in the controlled brakesystem is initiated without the pedal being applied (ABS, ESP). Furtheradvantages of the invention are the following: high degree of safety,measurement of the motion start in the tandem master cylinder and, thus,a directly plausible signal. In addition, there is a high degree ofaccessibility in the vehicle. Further, an adjustment is also possibleretroactively. The signal transmitter of the invention is favorable interms of costs, and there are no disturbing forces at the pedal.

[0004] The invention is not necessarily restricted to the operation of abrake light; other applications are also feasible where the position ofa piston in a cylinder shall be evaluated in a lowcost manner foractuating assemblies arranged downstream. A signal is sent to a controldevice or a plurality of control devices (ABS or other devices), whichis in a direct relation to the movement of a tandem master cylinderpiston and, thus, of the brake pedal as well. This signal may preferablybe used for operating the stoplights.

[0005] There are several possibilities for installing the sensor withinthe master cylinder. Thus, the magnet may, for example, be arrangedbeside the Hall element in the wall of the housing. This arrangement ise.g. possible when the piston is made of a magnetic material or isprovided with such a material at certain points. When the piston changesits position, the magnetic field existing between the magnet and theHall element will also be changed, thereby possibly triggering adisplay. Particularly the combination of features of claim 2 isadvisable in an advantageous improvement. In this feature, the magneticzone on the outside surface of the piston is active. This zone may beproduced by locally magnetizing the piston in as far as this piston iscomposed of a magnetizable material. The local magnetization may,however, also be employed when the magnetic zone is arranged in thehousing of the cylinder in the vicinity of the Hall element.

[0006] A particularly simple solution is achieved by applying thecombination of features of claim 3. In this case, the piston may alsoconsist of a non-magnetizable material such as plastics or aluminum.Further, very high magnetic fields may be produced this way, possiblyacting locally on the associated Hall element.

[0007] In an improvement of the invention according to claim 4, not onlythe piston but also the housing may be manufactured from anon-magnetizable material. The result is that the material of thepiston-and-cylinder assembly will not disturb the course of the magneticfield.

[0008] The position indicator of the invention may be improved to amajor degree in an improvement of the present invention by theprovisions of claim 5. Both the Hall element and the magnet is kept freefrom pressure forces so as to minimize the mechanical load on theseparts mounted into the assembly. Another advantage of this provisionresides in that weakening of the housing due to the arrangement of anaccommodating bore for a plug will not entail shortcomings because theaffected portion of the cylinder housing is largely free from pressureforces.

[0009] To be able to adapt the Hall sensor as simply as possible tovarious types of vehicles and to facilitate the exchange of a defectivesensor, it is advisable to apply the combination of features accordingto claim 6 in a further development of the invention. Thus, it is easilypossible by replacement of a plug to additionally adapt the Hall elementand the evaluating circuit to the parameters of the vehicle type or toexchange the mentioned components.

[0010] There is the possibility of slipping the plug into a radialthrough hole in the wall of the cylinder housing. No major drawbacks arecaused by the fact that this opening is arranged in a non-pressurizedarea of the cylinder. According to an improvement of the invention,however, it is recommended according to the combination of features inclaim 7 to configure the accommodating bore for the plug as a (stepped)blind-end bore. The result is that the machined inside wall of thecylinder is not punctured so that a smooth inside surface that isnecessary for a good operation of the cylinder is maintained.

[0011] According to the teachings of the invention, the sensor may alsobe employed in a tandem master cylinder. Likewise, several sensors in amaster cylinder of this type can be associated with the individualpistons. This may be done, for example, with a view to monitoring thatboth cylinders cover the same distance, e.g. for monitoring thecylinders with respect to errors in the mode of operation.

[0012] The electric signals produced by the position indicator of theinvention can be evaluated comparatively easily. Because the outputsignal of the sensor has a roughly sinusoidal course when the magnetpasses the Hall element, it is possible to deduce the instantaneousposition of the piston from the respective output voltage. This way, aswitching operation can be performed when the piston has covered apredetermined distance, with the output signal of the sensor havingreached a predetermined threshold value starting from a firstpredetermined threshold value.

[0013] An embodiment of the present invention is explained in thefollowing by way of the accompanying drawings. In the drawings,

[0014]FIG. 1 shows a tandem master cylinder equipped with the positionindicators of the invention.

[0015]FIG. 2 and FIG. 3 show a greatly simplified crosssectional view ofthe embodiment of a magnet attached to the piston.

[0016] The design and mode of operation of master cylinders isappropriately described in literature (cf. for example, inBremsen-Handbuch (Brake Handbook) by Autohausverlag GmbH Ottobrunn closeto Munich, edition 9.1) and, therefore, will not be described once more.In the following, the design of the master cylinder illustrated in FIG.1 is only dealt with to the extent necessary with respect to theinvention.

[0017]FIG. 1 shows a tandem master cylinder wherein housing 1 of thecylinder encloses two pistons 3, 4 arranged one behind the other. Acylindrical hollow space 20 that is delimited by housing 1 is referredto as cylinder in the following. The front piston 3 has an annularrecess 5, which is connected to the port 7 of the non-illustrated supplyreservoir by way of a breather 6. This relieves the annular recess 5from pressure so that basically ambient pressure of the housing 1prevails there. A cylinder opening 8 is inserted into the bottom of theannular recess 5 at an appropriate location, into which opening amagnetic metallic pin 9 is inserted as a magnet. The housing 1 at thebottom of FIG. 1 has a projection extending in a radial direction inwhich a stepped blind-end bore 11 is provided. This blind-end boreaccommodates a plug 12, which carries the Hall element (not shown) atits end that is at the top in FIG. 1. It is important that the blind-endbore 11 does not extend into the cylinder interior so that the smoothinside surface of the cylinder interior is not interrupted.

[0018] Hall element and magnet 9 are now arranged to each other in sucha way that with a movement of the front piston 3, the voltage that isoutput by the Hall element, starting from a maximum, will decline,thereby causing an evaluating circuit arranged in plug 12 to respond topredetermined voltage values of the declining output voltage of the Hallelement. The result is an abrupt change of voltage at the output of theplug 12 when the piston 3 moves through a defined range of the pistontravel. By variation of the response values of a trigger circuitdisposed in the evaluating circuit, it is possible to align the voltagevariation with respect to the position of the piston so that it can beadjusted quite precisely at what location of the piston travel theposition indicator responds, for example, in order to switch on a brakelight.

[0019]FIGS. 2 and 3 show possible embodiments of the magnet 9illustrated in FIG. 1. Magnet 9 is shaped as a cylindrical metal pin andmounted at bottom 15 of the annular recess 5. An elongated hole 16arranged in the front piston 3 can still be seen in FIGS. 2 and 3.

[0020]FIG. 3 shows a modified embodiment of the magnet in the form of anannular portion 18 being arranged in a corresponding recess at bottom 15of the annular recess 5.

[0021] Similar to the sensor described hereinabove, a sensor of thistype may also be installed optionally or additionally into the housing 1opposite the rear piston 4. It is only essential in this regard thatthis sensor is so arranged that the magnet connected to the piston 4 isdisposed in the pressureless zone of the interior of cylinder 1.

[0022] Therefore, the invention can be described briefly as follows: Thesignal describing the position of the piston is produced by means ofnon-contact sensing, preferably by means of a Hall element. A metalliccomponent (which may also be a magnet) is fitted to one of the tandemmaster cylinder pistons. The zone at the tandem master cylinder pistonis preferably pressureless. A sensor element (Hall sensor or Hall switchor element with a similar signal generation) is fitted to the tandemmaster cylinder housing in the same zone. Preferably, the element isincorporated in a zone, which remains without pressure over the entirestroke of the tandem master cylinder piston.

[0023] In an extended feature of the invention, there is the possibilityof calibrating the function limits in the installed condition. Thesensor element can be combined with a plug on the vehicle and may bedesigned so that it permits being exchanged in the vehicle. The resultis a high degree of safety in measuring the start of motion in thetandem master cylinder. A directly plausible signal is, in turn,achieved herefrom. The master cylinder is easily accessible in thevehicle. Further, retroactive adjustment is possible, which is veryfavorable with regard to costs. Also, disturbing forces at the pedal areeliminated. It is possible to produce a signal without interrupting theclosed system in the tandem master cylinder.

1. Position indicator for displaying the position of a piston (3) withina cylinder (1) in a cylinder-and-piston assembly (1, 3), preferably fora controlled brake system for automotive vehicles, characterized in thatthe cylinder-and-piston assembly is a master cylinder of a brake system,in that a Hall element of a Hall sensor is inserted into the cylinderwall (1) of the master cylinder, and in that a magnetic zone (9) isarranged in the piston-and-cylinder assembly in such a way that the Hallelement responds to the movement of the piston in the cylinder. 2.Position indicator as claimed in claim 1, characterized in that themagnetic zone (9) is arranged on the outside peripheral surface (15) ofthe piston (3) and is preferably formed of a magnet (9) connected to thepiston.
 3. Position indicator as claimed in claim 2, characterized inthat the magnet is inserted into a corresponding recess (8) in thepiston (3), with the magnet being preferably formed of a radiallyinserted magnetic circular cylinder (9) or a tangentially arrangedannular portion (18).
 4. Position indicator as claimed in any one ofclaims 1 to 3, characterized in that the piston (3) and/or the housingforming the cylinder is made of a non-magnetizable material, inparticular aluminum.
 5. Position indicator as claimed in any one ofclaims 1 to 4, characterized that the magnet is arranged in a portion ofthe piston at said, which is acted upon by the ambient pressure of thecylinder inside the cylinder.
 6. Position indicator as claimed in anyone of the preceding claims, characterized that the Hall element andpreferably an evaluating circuit that processes the signals of the Hallelement are arranged in a plug (12), and the cylinder housing (1)includes a plug opening (8) for receiving at least part of the plug(12).
 7. Position indicator as claimed in claim 6, characterized thatthe plug opening (8) essentially is a through hole that is accessible ina radial direction from outside, and the cylinder housing (1) comprisespreferably a radial projection (10) for engagement by the plug opening(8).
 8. Position indicator as claimed in any one of the precedingclaims, characterized that the master cylinder is a tandem mastercylinder.
 9. Position indicator as claimed in any one of claims 6 to 8,characterized that the evaluating circuit includes a trigger circuitwhich is triggered in dependence on defined voltage threshold values atthe Hall element, and the threshold values of the trigger circuit areadjustable for adapting the signal release in relation to the pistonposition.
 10. Position indicator as claimed in any one of the precedingclaims, characterized that it actuates a brake light switch.